LCD devices can generally be classified into two types depending on the type of the light source used. One is a transmissive LCD device and the other is a reflective LCD device. The transmissive LCD device displays a color image by irradiating artificial light from a back light, which is positioned behind a liquid crystal panel. The other is a reflective LCD device which displays a color image by controlling a transmittance of the light according to an alignment of the liquid crystal by reflecting ambient light or artificial light. Because the transmissive LCD device uses an artificial light source such as the back light, it can display a bright image in dark surroundings but it has a high power consumption. The reflective LCD device depends on ambient light or an external artificial light source for its light source and accordingly it has lower power consumption than the transmissive LCD device but it is not suitable for dark surroundings. A third type, the transflective LCD device, which has characteristics of both the transmissive and reflective LCD device, has been suggested as a combination of the first two types.
However, there exist drawbacks of the transflective LCD device. For example, its manufacturing steps are complicated. Transflective electrodes are usually formed by partially covering thin metallic film (reflective electrode) on an indium-tin oxide (ITO) layer (transmissive electrode). Integration of such electrodes requires extra processing steps that usually lead to poor yield.
FIG. 8 illustrates the structure of a conventional active-matrix transflective liquid crystal display device. An insulating substrate 801 is provided, on top of which is deposited a buffer layer 802. An active layer of a thin-film transistor (TFT) comprising electrode regions 807 and 809, and a channel region 808 are formed within the polycrystalline silicon layer. The gate oxide layer 803 is formed on and covered the active regions (807, 808 and 809). Two insulation layers 804a and 804b made of low-temperature oxide (LTO) are formed on the gate oxide layer 803. A gate electrode 810 of the TFT is formed on the gate oxide layer 803 and buried within the first insulation layer 804a. A transparent electrode 806 made of indium tin oxide (ITO) is formed at the location as illustrated. The transparent electrode 806 is electrically connected to one electrode region 809 of the TFT via a metal electrode 805 made of aluminum.